The brakes of a heavy aircraft are not that different from the brakes of a car. In the braking system of a typical car, the brake pads or friction pads are pressed against a rotor which rotates at the speed of the wheels. When the driver hits the brakes, brake fluid which is under pressure is sent to a piston, which moves the pads against the rotor and stops the wheel from spinning.
Because of its simplicity, light aircraft also use a similar system. This type of brake is most known as single-plate disc brakes. The aircraft brakes must absorb a huge amount of energy during landing and in the event of a rejected takeoff.
Due to the amount of energy involved, aircraft brakes need to be robust and reliable. There are a few reasons why such a braking system might not be the best idea for a larger aircraft. One is that such a system cannot simply dissipate the required energy.
We can do a simple calculation for a Cessna 172 and an Airbus A320 for comparison. As brakes convert kinetic energy into heat, we could calculate the energies involved when both aircraft come to land. We would assume that the Cessna 172 has a mass of 700 kg and a landing speed of 32 m/s.
And for the A320, a mass of 64,000 kg and a speed of 70 m/s. A Cessna 172 example KE = 1⁄2 x m x v^2 KE = 1⁄2 x 700 x 30^2 KE = 315,000 J An Airbus A320 example KE = 1⁄2 x m x v^2 KE = 1⁄2 x 64000 x 70^2 KE = 156,800,000 J Based on the calculations, the brakes of an Airbus A320 must absorb almost 500 times more energ.
